Dielectric properties of annealed onion-like carbon composites in microwave region

Abstract

The onion-like carbon composites prepared according to different technologies were studied by means of broadband dielectric/electric spectroscopy in a wide temperature range from 300 to 450 K. The value of complex dielectric permittivity of composites strongly increases after annealing. From complex dielectric spectra, complex impedance spectra and distribution of relaxation times were calculated. After annealing of composites on cooling the asymmetricity of distribution of relaxation times strongly increases. Annealed composites exhibit only a weak temperature dependence of microwave properties and are promising candidates for electromagnetic shielding materials.